The invention relates to a switch arrangement for switching electrical functions with switches having at least two electric contact elements, and it especially concerns an arrangement of at least two switches wherein the two switches are located adjacent one another and are so constructed as to be operated essentially simultaneously in response to a single finger press or the like by the operator, such arrangement, for example being desireable for use in controlling the movement functions of an apparatus for supporting patients.
In the case of patient supporting apparatus, motorized adjustable movement functions for changing the positions of patients frequently are switched by existing double electrical switch circuits independent of one another. If a fault occurs in one of the electrical circuits the movement of the support apparatus is immediately stopped or not carried out. The reason for this is that any danger to a patient from a faulty movement function of the supporting apparatus must be prevented.
It is already known to provide, in a switch or service unit for a patient support apparatus, two switches for operating the separate switch circuits, in which case the desired movement function of the patient support apparatus can only be carried out if both of the switches are actuated. This especially provides an assurance that a movement of the support apparatus can be interrupted in any event, even if in one of the switches the contact elements at a given time remain stuck to one another or the like. This solution involves however an increased surface requirement for the switch unit, and therewith a corresponding constructional size, since this switch unit for the plurality of movement modes of the support apparatus has a corresponding plurality of switches whose operating elements can not arbitrarily be made smaller. Moreover, the operation of two switches at the same time is troublesome.
The invention has as its object the provision of a switch arrangement of the aforementioned type which with regard to the avoidance of the previously described disadvantages has a low space requirement and makes possible an easy operation.
This object is solved in accordance with the invention in that at least one switch is made as a foil switch having a flexible base foil carrying one contact element and a switch element, particularly a switch foil, having an opposing contact element and elastically deflectable toward the contact element of the base foil, and in that the other switch is arranged behind the foil switch in the keying direction, so that the second switch is operable by a pressure on the foil switch which exceeds the pressure needed to operate the foil switch.
Therefore, for a switch arrangement according to the invention, for example in a switch device, only the area associated with the key surface of the foil switch is required. Also, the heigth of the switch arrangement in the keying direction is very small, since the foil switch itself requires only a small amount of space. By pressing on the foil switch it itself is first actuated. By further pressure on the flexible foil switch the electrical switch arranged below or behind it can then also be operated. This rear switch likewise can be made as a foil switch or also can be made as a mechanical pressure switch. In the case of several rearwardly arranged foil switches it is advantageous, with respect to the heigth of the entire switch arrangement, if the base foil of the forwardly lying foil switch forms the switch foil of the following foil switch in the keying direction.
Basically, it is possible to connect the switch arrangement of the invention in a switch circuit so that all of the switches in the same switch circuit are in series with one another. For the above-mentioned special application it is preferable if the switches are arranged in separate switch circuits which are connected with the inputs of an AND-gate whose output signal first controls a movement function of the support apparatus. So long as not all of the switches are simultaneously engaged the movement function of the support apparatus can be interrupted in all events, even if in one of the switches the contact elements remain unwantedly closed, as for example in the case of their being stuck to one another.
The invention is explained in more detail in the following description, in connection with the accompanying drawings, with respect to embodiments of the invention.